Human Reproduction

Humans reproduce sexually, with both males and females contributing genetic material to offspring. The process involves several key stages:

1. Gametogenesis: The production of gametes, or sex cells, through meiosis. In males, this process occurs in the testes and produces sperm cells. In females, it occurs in the ovaries and produces ova (eggs).
   
2. Fertilization: The fusion of a sperm cell with an ovum in the fallopian tube. This results in the formation of a zygote, the fertilized egg.
   
3. Implantation: The zygote travels down the fallopian tube and implants in the endometrium of the uterus. Here, it develops into a blastocyst, a hollow ball of cells.
   
4. Embryonic Development: The blastocyst continues to develop into an embryo, which undergoes a series of stages and processes, including gastrulation, neurulation, and organogenesis.
   
5. Fetal Development: After the embryonic stage, the developing organism is called a fetus. During this stage, the fetus continues to grow and differentiate, forming all of its organs and tissues.
   
6. Parturition: The process of childbirth, in which the fetus is expelled from the uterus. This typically occurs around 38-40 weeks after fertilization.
   
7. Postpartum Care: The period after childbirth, during which the mother and newborn recover and bond.

Key Points:

• Human reproduction is a complex process that involves many different organs and hormones.
• It is essential for the continuation of the human species.
• Understanding the process of human reproduction can help individuals make informed decisions about their reproductive health and family planning.

Exercise

1. Fill in the blanks: 

(a) Humans reproduce _____________ (asexually/sexually) 

(b) Humans are _____________ (oviparous, viviparous, ovoviviparous) 

(c) Fertilisation is _____________ in humans (external/internal) 

(d) Male and female gametes are _____________ (diploid/haploid) 

(e) Zygote is _____________ (diploid/haploid

(f) The process of release of ovum from a mature follicle is called _____________ ,    

(g) Ovulation is induced by a hormone called _____________ 

(h) The fusion of male and female gametes is called _____________ 

(i) Fertilisation takes place in _____________ 

(j) Zygote divides to form _____________which is implanted in uterus. 

(k) The structure which provides vascular connection between foetus and uterus is called _____________ ) 

Ans : 

(a) Sexually.

(b) Viviparous.

(c) Internal in humans.

(d) Haploid.

(e) Diploid.

(f) TOvulation.  

(g) Luteinizing hormone (LH).

(h) Fertilization.

(i)Fallopian tube.  

(j) Blastocyst

(k) Umbilical cord

2. Draw a labelled diagram of male reproductive system

Ans : 

3. Draw a labelled diagram of female reproductive system.

Ans : 

4. Write two major functions each of testis and ovary.

Ans : 

Testes

1. Sperm production: The testes are responsible for producing sperm, the male gametes that are essential for fertilization.
2. Testosterone production: The testes also produce testosterone, a male sex hormone that is responsible for male sexual development and characteristics, such as muscle mass, bone density, and facial hair.

Ovaries

1. Ovulation: The ovaries produce and release eggs (ova) during ovulation. This process is essential for reproduction.
2. Hormone production: The ovaries produce hormones such as estrogen and progesterone. These hormones regulate the menstrual cycle, control secondary sex characteristics, and play a role in pregnancy.

5. Describe the structure of a seminiferous tubule. 

Ans : 

Seminiferous tubules are the coiled structures within the testes where sperm production takes place. They are lined with various cell types, each playing a specific role in spermatogenesis:

1. Sertoli Cells: These tall, columnar cells provide structural support and nourishment to developing sperm cells. They also secrete hormones and play a role in the regulation of spermatogenesis.
2. Spermatogonia: These are the stem cells that undergo mitosis to produce primary spermatocytes.
3. Primary Spermatocytes
4. Secondary Spermatocytes: These cells undergo meiosis II to produce spermatids.
5. Spermatids: These immature sperm cells undergo spermiogenesis, a process of differentiation, to mature into spermatozoa.

6. What is spermatogenesis? Briefly describe the process of spermatogenesis.

Ans : 

Spermatogenesis is the process of sperm production in the testes of male animals. It involves a series of cell divisions and differentiations that ultimately result in the formation of mature sperm cells.

Here’s a brief overview of the process:

1. Spermatogonia: The process begins with spermatogonia, which are diploid stem cells located in the seminiferous tubules. 
2. Primary Spermatocyte: Some spermatogonia differentiate into primary spermatocytes, which are also diploid.
3. Meiosis I: Primary spermatocytes undergo meiosis I, a type of cell division that reduces the number of chromosomes to haploid. 
4. Meiosis II: Secondary spermatocytes undergo meiosis II, further reducing the chromosome number and producing four haploid spermatids.
5. Spermiogenesis: Spermatids differentiate into mature sperm cells, a process called spermiogenesis. 
6. Storage and Release: Mature sperm are stored in the epididymis and are released during ejaculation.

7. Name the hormones involved in regulation of spermatogenesis

Ans : 

Testosterone: Produced by the Leydig cells in the testes, testosterone is the primary hormone responsible for stimulating spermatogenesis.

Follicle-stimulating hormone (FSH): Produced by the anterior pituitary gland, FSH stimulates the Sertoli cells in the testes to support spermatogenesis. It also promotes the production of inhibin, a hormone that regulates the production of FSH and testosterone.

Luteinizing hormone (LH): Also produced by the anterior pituitary gland, LH stimulates the Leydig cells to produce testosterone.

Inhibin: Produced by the Sertoli cells, inhibin provides negative feedback on the production of FSH and LH by the anterior pituitary gland, helping to regulate spermatogenesis.

8. Define spermiogenesis and spermiation.

Ans : 

Spermiogenesis is the final stage of spermatogenesis, where spermatids differentiate into mature sperm cells. It involves a series of morphological changes

Spermiation is the process by which mature sperm cells are released from the Sertoli cells into the lumen of the seminiferous tubule. This occurs after spermiogenesis is complete.

9. Draw a labelled diagram of sperm.

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10. What are the major components of seminal plasma?

Ans : 

Seminal plasma is the fluid that carries sperm cells during ejaculation. It is produced by various glands in the male reproductive system.:

1. Fructose
2. Citric acid: A component of the Krebs cycle, which produces energy for sperm.
3. Alkaline substances: These substances help to neutralize the acidic environment of the vagina, which is harmful to sperm.
4. Proteins: Proteins in seminal plasma help to coagulate the semen after ejaculation, forming a plug that helps to retain sperm in the female reproductive tract.
5. Enzymes: Enzymes in seminal plasma help to liquefy the semen after ejaculation, allowing sperm to swim freely.
6. Prostaglandins: Hormones that stimulate uterine contractions and help to propel sperm towards the ovum.
7. Inorganic ions: Ions such as sodium, potassium, calcium, and magnesium play a role in sperm motility and fertilization.

11. What are the major functions of male accessory ducts and glands?

Ans: 

Male accessory ducts and glands play essential roles in the production, storage, and delivery of sperm. They also contribute to the composition of seminal plasma, the fluid that carries sperm during ejaculation.

Major Functions:

1. Storage and Transportation of Sperm:
   • Epididymis: Stores sperm and allows them to mature.
   • Vas deferens: Transports sperm from the epididymis to the ejaculatory ducts.
2. Production of Seminal Plasma:
   • Seminal vesicles: Produce a fluid that contains fructose (for energy), prostaglandins (for uterine contractions), and other substances that nourish and protect sperm.
   • Prostate gland: Produces a fluid that contains enzymes, citric acid, and other substances that contribute to the alkalinity and composition of seminal plasma.
3. Ejaculation:
   • Ejaculatory ducts: Carry sperm and seminal plasma from the seminal vesicles and prostate gland to the urethra.
   • Urethra

12. What is oogenesis? Give a brief account of oogenesis.

Ans : 

It involves a series of cell divisions and differentiations that ultimately result in the production of a mature ovum.

Here’s a brief account of oogenesis:

1. Oogonia: Oogenesis begins with oogonia, which are diploid stem cells present in the ovaries from birth. These cells undergo mitotic division to produce more oogonia.
2. Primary Oocyte: Some oogonia differentiate into primary oocytes, which are also diploid. Primary oocytes enter meiosis I but remain arrested in the prophase stage until puberty.
3. Meiosis I: At puberty, a primary oocyte completes meiosis I, producing a secondary oocyte and a polar body. The secondary oocyte receives most of the cytoplasm, while the polar body is small and non-functional.  
5. Meiosis II: The secondary oocyte starts meiosis II but remains arrested in metaphase II until fertilization occurs.
6. Fertilization: If a sperm cell penetrates the secondary oocyte, meiosis II is completed, producing a mature ovum and a second polar body.

13. Draw a labelled diagram of a section through ovary.

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14. Draw a labelled diagram of a Graafian follicle?

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15.  Name the functions of the following: 

(a) Corpus luteum (b) Endometrium (c) Acrosome (d) Sperm tail (e) Fimbriae

Ans : 

(a) Corpus luteum: Produces progesterone and estrogen to maintain the uterine lining for implantation of a fertilized egg. It also plays a role in regulating the menstrual cycle.

(b) Endometrium: The inner lining of the uterus that thickens and prepares for the implantation of a fertilized egg. If no implantation occurs, the endometrium is shed during menstruation.

(c) Acrosome: A cap-like structure at the head of a sperm cell that contains enzymes necessary for penetrating the ovum.

(d) Sperm tail: A flagellum that enables the sperm cell to swim and reach the ovum.

(e) Fimbriae: Finger-like projections at the end of the fallopian tubes that help to capture the ovum released from the ovary and direct it towards the uterus.

16. Identify True/False statements. Correct each false statement to make it true. 

(a) Androgens are produced by Sertoli cells. (True/False) 

(b) Spermatozoa get nutrition from Sertoli cells. (True/False) 

(c) Leydig cells are found in ovary. (True/False) 

(d) Leydig cells synthesise androgens. (True/False) 

(e) Oogenesis takes place in corpus luteum. (True/False) 

(f) Menstrual cycle ceases during pregnancy. (True/False) 

(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)

Ans : 

(a) False. Androgens are produced by Leydig cells, not Sertoli cells.

(b) True. Spermatozoa get nutrition from Sertoli cells.

(c) False. Leydig cells are found in the testes.

(d) True. Leydig cells synthesize androgens.

(e) False. Oogenesis takes place in the ovaries, not the corpus luteum.

(f) True. Menstrual cycle ceases during pregnancy.

(g) True. Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.

17. What is menstrual cycle? Which hormones regulate menstrual cycle?

Ans : 

Menstrual Cycle

The menstrual cycle is a series of hormonal changes and physical events that occur in a woman’s body each month, preparing her for potential pregnancy. It typically lasts around 28 days, although this can vary from person to person.

Hormones Regulating the Menstrual Cycle

Several hormones, primarily produced by the hypothalamus, pituitary gland, and ovaries, regulate the menstrual cycle. These include:

1. Follicle-Stimulating Hormone (FSH): Stimulates the growth and development of follicles in the ovaries, which contain eggs.
2. Luteinizing Hormone (LH): Triggers ovulation, the release of a mature egg from the ovary.
3. Estrogen: Produced by the ovaries, estrogen stimulates the thickening of the uterine lining (endometrium) to prepare for a potential pregnancy.
4. Progesterone: Also produced by the ovaries, progesterone helps maintain the thickened uterine lining and prepares the body for pregnancy.

18.What is parturition? Which hormones are involved in induction of parturition?

Ans : 

Parturition is the process of childbirth, also known as labor and delivery. 

Hormones Involved in Induction of Parturition

Several hormones play a role in initiating and regulating the process of parturition:

1. Oxytocin: Released from the posterior pituitary gland, oxytocin stimulates contractions of the uterine muscles, helping to expel the fetus.
2. Prostaglandins: These hormones, produced by the fetal membranes and uterine tissues, also stimulate uterine contractions and help to soften the cervix.
3. Cortisol: Released from the fetal adrenal glands, cortisol helps to initiate the production of prostaglandins, which in turn stimulate labor.
4. Relaxin: Produced by the placenta, relaxin helps to soften the cervix and pelvic ligaments, making it easier for the baby to pass through the birth canal.

19. In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?

Ans : 

That’s a harmful and inaccurate belief. The gender of a child is determined by the sperm, not the egg. Men carry the X and Y chromosomes that determine the sex of the offspring. Therefore, it’s not fair to blame women for the gender of their children.

Here are some reasons why this belief is incorrect:

• Genetics: The sex of a child is determined by the sperm cell that fertilizes the egg. If the sperm carries an X chromosome, the child will be female. 
• Biology: The production of sperm and the determination of their sex are complex biological processes that are not under the control of either parent.
• Social and Cultural Factors: The belief that women are responsible for the gender of their children is often rooted in social and cultural biases that perpetuate gender inequality.

20.How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?

Ans : 

A human ovary typically releases one egg per month. 

If a mother gives birth to identical twins, it means that a single fertilized egg split into two embryos. Therefore, only one egg would have been released. Identical twins share the same genetic material because they develop from the same egg.

If the twins born were fraternal, it means that two separate eggs were fertilized by two different sperm. In this case, two eggs would have been released from the ovary. Fraternal twins are genetically different because they develop from separate eggs.

21. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies? 

Ans : 

It’s difficult to say exactly how many eggs were released by the ovary of a female dog that gave birth to 6 puppies without knowing more about the dog’s reproductive history. However, it’s likely that more than 6 eggs were released.